This invention generally relates to heat transfer systems and more particularly relates to systems for cooling LED arrays.
Many applications which use infrared cameras depend on infrared light emitted from LED arrays to illuminate the subject whose image is being captured by the infrared camera. Infrared cameras are often used in imaging applications associated with vehicle safety systems to determine the presence (or absence) of a passenger in one or more locations within a vehicle. Infrared imaging systems are also used in automobile applications in what is known as “driver gaze systems.” Driver gaze systems are systems that monitor driver eye and head movement to determine if the driver is falling asleep or otherwise becoming inattentive to his driving responsibilities.
By their nature, infrared cameras can operate at an optimal efficiency only if the light received by the camera falls within an optimum wavelength range. If an infrared camera is operated outside of its optimum wavelength range, its efficiency degrades significantly. For example, many infrared cameras operate optimally in a wavelength band centered around 940 nm. In order to obtain the optimal performance from the infrared camera, the infrared LED array used to illuminate the subject, should have a spectral irradiance maximum centered on or about the 940 nm wavelength point. Although such ideal matching between camera and LED array can be achieved in the laboratory setting, such ideal conditions cannot typically be met within a vehicle passenger compartment inasmuch as unregulated passenger compartment temperatures can vary anywhere from −40 degrees C. to 85 degrees C. and LED arrays have a significant wavelength shift vs. temperature dependence (typically about 0.25 nm/° C.). When a vehicle HVAC system is operational, typical cabin temperatures vary within a much narrower range (typically 22 degrees C.+/−5 degrees C.).
The present invention takes advantage of the moderating temperatures provided by the HVAC system within the vehicle to moderate the temperature of the LED array.